Determining the exact location of a mobile device (e.g., a smart phone operated by a user) in an environment can be quite challenging, especially when the mobile device is located in an urban environment or is located near or within a building. Imprecise estimates of the mobile device's position may have life or death consequences for the user of the mobile device since the imprecise position estimate can delay emergency personnel response times. In less dire situations, imprecise position estimates can lead a user to the wrong area in an environment or can impair other uses of an estimated position of a mobile device.
By way of example, an operational environment 100 in which systems and methods for estimating a position of a mobile device may operate is shown in FIG. 1. The environment 100 includes a network of terrestrial transmitters 110, at least one mobile device 120, and a server 130. Each of the transmitters 110 and the mobile device 120 may be located at different altitudes or depths that are inside or outside various buildings 190. Positioning signals 113 and 153 are respectively transmitted from the transmitters 110 and satellites 150 and later received by the mobile device 120 using known transmission technologies. The transmitters 110 may transmit the signals 113 using one or more common multiplexing parameters—e.g. time slot, pseudorandom sequence, frequency offset, or other, as is known in the art or otherwise disclosed herein. In some embodiments of FIG. 1, each transmitter 110 may include atmospheric sensors (e.g., a pressure sensor and a temperature sensor) for generating measurements of atmospheric conditions (e.g., pressure and temperature) that can be used to estimate an unknown altitude of the mobile device 120, as described later. The mobile device 120 may take different forms, including a mobile phone or other wireless communication device, a portable computer, a navigation device, a tracking device, a receiver, or another suitable device that can receive the signals 113 and/or 153. Examples of possible components in the transmitters 110, the mobile device 120, and the server 130 are shown in FIG. 12 and discussed in the ‘Other Aspects’ section towards the end of this disclosure.
The network of transmitters 110 and/or the satellites 150 form a positioning system that can be used to determine an initial estimate of the position of the mobile device 120—e.g., where the estimate of the position is represented in terms of: latitude, longitude, and/or altitude coordinates; x, y, and/or z coordinates; angular coordinates; or other representations. Various techniques for estimating the position of the mobile device 120 can be used, including trilateration, which is the process of using geometry to estimate the position of the mobile device 120 using distances traveled by different “positioning” (or “ranging”) signals (e.g., signals 113 or signals 153) that are received by the mobile device 120 from beacons (e.g., the terrestrial transmitters 110 or the satellites 150, respectively). If position information like the transmission time and reception time of a positioning signal from a beacon are known, then the difference between those times multiplied by speed of light would provide an estimate of the distance traveled by that positioning signal from that beacon to the mobile device 120. Different estimated distances corresponding to different positioning signals from different beacons can be used along with position information like the locations of those beacons to estimate the initial position of the mobile device 120, as is well-known.
Although the network of transmitters 110 and/or the satellites 150 can be used to determine an initial estimate of the position of the mobile device 120, the resulting initial estimate of the position of the mobile device 120 may only be an approximate position with varying degrees of uncertainty that precludes any conclusion as to whether the mobile device 120 is inside or outside the building 190, especially in urban environments where multipath propagation of positioning signals extends the lengths of estimated distances over which particular signals travel. The uncertainty is typically represented by a well-known location confidence value that estimates one or more possible differences between the estimated position and the true position of the mobile device, which can convey that the mobile device 120 could be either inside the building 190 or outside.
Knowing that the mobile device 120 is actually inside the building 190 or actually outside has many valuable uses, including: (i) uses for detecting opportunities to calibrate a pressure sensor of the mobile device 120 that is used for future altitude estimation of the mobile device 120; (ii) uses for detecting if a mobile device is inside a particular building to improve emergency response times by reducing the search area in which the mobile device resides; (iii) uses for detecting if a mobile device is inside a particular building to retrieve particular information about that building such as a building map or information used to resolve a floor level at which the mobile device is located or other information; (iv) uses for detecting if a mobile device is inside a particular building to collect and store information about that building for later use in different applications that are known in the art; (v) uses for detecting if a mobile device is outside to improve emergency response times by reducing the search area in which the mobile device resides; (vi) uses for detecting if a mobile device is outside to collect and store information about the outside area for later use in different applications that are known in the art; or (vii) other uses. However, determining whether the mobile device 120 is actually inside the building 190 or actually outside with high degrees of certainty is a significant and difficult technical problem that must be solved. Solutions for improved detection of an indoor or outdoor position of a mobile device are described herein.